1. Field of the Invention
The present invention relates to apparatus for migration imaging using a mixture of differently colored electrophotosensitive particles, and more particularly to improved apparatus of the type which electrically addresses discrete picture elements (pixels) of such mixture in an imagewise timed relation with exposure of the pixels by time-separated, differently-colored, light pulses.
2. Description of the Prior Art
Photoelectrophoretic migration imaging involves the light image exposure of a liquid suspension, comprising dielectric liquid carrier and differently-colored, photoconductive toner particles, while between electrodes that provide a migration inducing field. U.S. Pat. No. 3,140,175 to Kaprelian discloses early procedures and apparatus of this type. In operation, the suspended toner particles attain a charge and migrate from the suspension to one of the electrodes. Upon exposure the illuminated particles migrate to the other electrode in accordance with the exposing light image pattern. Various embodiments for photoelectrophoretic migration imaging have been subsequently proposed (e.g., see U.S. Pat. No. 3,384,565). Recently a photoimmobilized electrophoretic migration imaging method has been described wherein the light-exposed, photoconductive toner particles are retained at the electrode to which they first migrate and unexposed particles change charge and migrate to the other electrode (see, e.g., U.S. Pat. No. 3,976,485).
Certain difficulties have arisen during efforts to commercialize such migration imaging systems. For example, high density images are difficult to attain in such systems. Further, in color imaging using this technique, it would be useful to have capabilities for color adjustment without inserting filter elements and image sense reversal without the forming of internegatives. Also, it is envisioned that office systems of the future may utilize image transmission, and it is not apparent that traditional, optically-addressed copiers can provide such a feature.
In view of one or more of the problems and/or desired capabilities noted above, there have been described in literature proposals for electro-optically-addressable photoelectrophoretic imaging systems. For example U.S. Pat. No. 3,663,396 and British Pat. No. 1,341,690 respectively disclose electronic address of a color cathode ray tube and an electro-luminescent panel used as the exposure source for such an imaging system. Another electro-optical approach is disclosed in U.S. Pat. No. 4,058,828. In this device a multicolor laser beam is scanned point by point across the imaging area and modulated according to the point-by-point color content of the image to be reproduced. These approaches offer the potential for improved density, color adjustment and electronic transmission of images; however, the exposure elements and control systems for such systems are fairly complicated and expensive.
Commonly assigned co-pending U.S. Application Ser. No. 821,114 entitled ELECTRONIC IMAGING USING MULTICOLOR ELECTROPHOTOSENSITIVE PARTICLES and filed Aug. 2, 1977 discloses an approach which has been found useful for obviating the above-described difficulties. In that approach, discrete pixels of migration imaging mixture are individually addressed by imagewise modulated electrical fields in timed relation to a series of differently colored light pulses. However in certain applications, for example those requiring high resolution, difficulties have been encountered from the viewpoint of fabricating the discrete electrode arrays used for addressing the imaging mixture.